1. Field
Aspects of the present disclosure relate to compounds, compositions including the same, fuel cell electrodes produced using the compounds or the compositions, fuel cell electrolyte membranes produced using the compounds or the compositions, and fuel cells including either fuel cell electrodes or fuel cell electrolyte membranes, or both fuel cell electrodes and fuel cell electrolyte membranes.
2. Description of the Related Art
Fuel cells that include a polymer electrolyte membrane operate at relatively low temperatures and may be manufactured in a small size. Thus, such fuel cells are expected to be used as energy sources in electric vehicles and distributed generation systems. Perfluorocarbon sulfonic acid-based polymer membranes, such as NAFION® membranes (available from E.I. du Pont de Nemours and Company), are commonly used as polymer electrolyte membranes for fuel cells. However, such polymer electrolyte membranes should be humidified in order to sufficiently conduct protons. In addition, to enhance cell system efficiencies, polymer electrolyte membranes should be operated at high temperatures, i.e., at least 100° C. However, moisture in the polymer electrolyte membrane is depleted and even evaporated at such temperatures, and thus, the effectiveness thereof is reduced.
To address such problems and/or other problems in the related art, non-humidified electrolyte membranes that operate at temperatures of at least 100° C. without humidification have been developed. For example, polybenzimidazole doped with phosphoric acid has been disclosed as a material for a non-humidified electrolyte membrane.
In regard to low-temperature perfluorocarbonsulfonate polymer electrolyte membrane fuel cells, hydrophobic electrodes including a water-repellent substance such as polytetrafluoroethylene (PTFE) have been introduced to prevent unwanted gas diffusion in an electrode (in particular in a cathode), which may be caused by water (product water) generated during electric power production in the electrode.
In regard to phosphoric acid fuel cells, which operate at temperatures of from 150 to 200° C., a liquid phosphoric acid electrolyte is used as an electrolyte. However, the liquid phosphoric acid included in a large amount in electrodes interferes with gas diffusion in the electrodes. Therefore, an electrode catalyst layer that includes polytetrafluoroethylene (PTFE) as a water repellent substance so as to prevent fine pores in the electrodes from being clogged by the phosphoric acid has been used.
In regard to fuel cells including a polybenzimidazole (PBI) electrolyte membrane, which uses phosphoric acid as a non-humidified electrolyte, in order to reduce contact between electrodes and the electrolyte membrane a method of impregnating the electrodes with a liquid phosphoric acid has been used, and a method of increasing the loading amount of metal catalysts has been used. However, such fuel cells do not exhibit improved properties.
When air is supplied to a cathode, activation takes about a week even if the electrode composition is optimized in a solid polymer electrolyte membrane doped with phosphoric acid. Although fuel cells can have improved efficiency and activation time can be decreased by replacing air with oxygen, use of oxygen is not preferable for commercialization reasons. In addition, a homogeneous polymer electrolyte membrane using the PBI is not satisfactory in terms of mechanical characteristics, chemical stability, or capability of retaining phosphoric acid. Thus, there is a need for further improvement.